1. Field of the Invention
The present invention relates to an imaging lens and an imaging device equipped with the imaging lens, and more particularly to a wide angle imaging lens suitable for use in an onboard camera, a camera for a portable terminal, a surveillance camera, and the like, using an imaging element, such as a CCD (Charge-Coupled Device), CMOS (Complementary Metal Oxide Semiconductor), or the like, as well as to an imaging device equipped with the imaging lens.
2. Description of Related Art
An extreme progress has recently been made in miniaturization and an increase in the number of pixels of an imaging element, such as a CCD and CMOS. In step with such a progress, miniaturization of a main body of imaging equipment having the imaging element has also advanced, and miniaturization of the imaging lens incorporated into the imaging equipment is also sought.
Meanwhile, in relation to an onboard camera or a surveillance camera, there has been sought a compact, inexpensive wide-angle lens which exhibits high weather resistance from outside air in a cold district to the inside of a vehicle compartment located in the tropics; which is usable over a wide temperature range; and which has a small F number.
Imaging lenses described in U.S. Pat. No. 7,023,628, Japanese Patent No. 2599312 and JP-A-61-123810 been known as the imaging lens of the foregoing field. U.S. Pat. No. 7,023,628 describes a fisheye lens consisting of five-grouped six lenses. Japanese Patent No. 2599312 describes a wide-angle lens which includes five-grouped six lenses or five-grouped seven lenses and which includes an aspheric lens. JP-A-61-123810 describes a wide-angle lens which is used for a compact camera of a surveillance camera and which consists of five-grouped six lenses or five-grouped seven lenses.
U.S. Pat. No. 7,023,628 describes a bright lens having an F number of 2, but the lens frequently uses a glass material whose refractive index exceeds a value of 1.9 and hence has a drawback of high cost. The lens described in Japanese Patent No. 2599312 uses an aspherical lens. When the lens is formed by using glass as a material, the lens also becomes expensive unfavorably. In addition to being insufficiently wide-angle and miniaturized, the lens described in JP-A-61-123810 forms a dark optical system having an F number of 2.8 to 4.